The invention concerns safety-relevant systems in motor vehicles and relates, in particular, to a redundant current supply having a diagnostic capability and a suppressor for improving the availability of such safety-relevant systems.
Important and/or safety-relevant systems in the motor vehicle sector, for example electronic braking systems or gear shifting systems in the area of passenger vehicles and utility vehicles, have to be provided with maximum availability in order to be able to ensure an emergency running capability of a motor vehicle, for instance, in the event of a failure or some other fault situation.
Therefore, in the case of such systems, inter alia for the current supply thereof, a redundancy is required in such a way that the current supply is routed via at least two separate paths, which are independent of one another, and, in the event of a failure of one path, an uninterrupted supply of an electronic control unit is ensured and an identification and an indication of this failure are possible.
In the case of known arrangements, this is achieved by decoupling the two paths via lines that can be switched over, by use of relay contacts, diodes and transistors, for example.
In the case of a decoupling of this type, however, a power loss occurs at the involved diode elements, which power loss is determined by the forward voltage of the diode and the load current flowing through the diode. Moreover, there is the possibility that after a changeover operation, the entire load current immediately flows through the still intact current path and is no longer divided—ideally in the ratio 1:1—between the at least two equivalent current supply branches present. This can lead to the occurrence of great peak powers in the diodes and consequently to a destruction of the diodes.
Particularly in the case of systems having a high current consumption, such as transmission controllers, for example, and/or high operating temperatures, therefore, the power losses that occur in semiconductor switching elements used for decoupling have to be minimized in order not to exceed the maximum permissible operating temperature of the semiconductor switching elements and, as a result, not to reduce the service life thereof.
Therefore, the invention is based on the object of providing a redundant current supply for safety-relevant systems in motor vehicles, which minimizes power losses occurring in semiconductor switching elements and limits the peak powers occurring therein.
According to the invention, a circuit arrangement for the redundant current supply of a load connected downstream is provided, the circuit arrangement including:
at least one first current path comprising a first switching element at which a first voltage is present on the input side;
at least one second current path comprising a second switching element at which a second input voltage is present on the input side;
at least one first control device, which is connected to the first current path and serves for controlling the first switching element;
at least one second control device, which is connected to the second current path and serves for controlling the second switching element; and
a common output terminal of the first and second current paths, at which a load supply voltage is output; wherein in a normal operating state, the first control device holds the first switching element in a conducting state and the second control device holds the second switching element in a conducting state, and further wherein in an abnormal operating state, depending on electrical properties of the first current path or of the second current path, one of the control devices which is situated in the current path having poorer electrical properties brings the switching element in this current path into a blocking state.
Preferably, the first and the second switching elements are power semiconductors, in this case advantageously a normally “off” n-MOSFET.
Particularly preferably, the first and the second control device, in each case, is constructed from identical and identically interconnected elements, is arranged in parallel with the first and the second switching elements, respectively, has a first input for putting and holding the first and the second switching elements, respectively, into/in the “on” state by means of a control unit, has a second input for detecting a current generated by the first and second switching elements, respectively, has a first output for controlling the switching state of the first and the second switching elements, respectively, depending on the current detected at the second input, and has a second output for the feedback of the switching state of the first and second switching elements, respectively, to the control unit and detection of the switching state by means of the latter.
The control by a microcontroller of an electronic control unit of the vehicle is advantageous in this case.
Particularly advantageously, the first and second current paths are decoupled by an internal diode, operated in the reverse direction, respectively of the first and the second switching elements.
Preferably, the electrical properties are the voltage at the first and the second current path and the internal resistance of the first and of the second current path, the poorer electrical properties are a higher internal resistance or a lower voltage, and the switching element in the lower-resistance current path is controlled to the conducting state and the switching element in the higher-resistance current path is controlled into the blocking state.
In this case, advantageously, a changeover to the lower-resistance current path is effected automatically and in a self-controlled fashion, and a changeover to the lowest-resistance current path is effected depending on the number of current paths present.
A method is also provided for the redundant current supply of a load connected downstream in a circuit arrangement, including at least one first current path including a first switching element at which a first voltage is present on the input side, at least one second current path including a second switching element at which a second input voltage is present on the input side, at least one first control device which is connected to the first current path and serves for controlling the first switching element, at least one second control device which is connected to the second current path and serves for controlling the second switching element, and a common output terminal of the first and second current paths, at which a load supply voltage is output. The method is characterized by the steps of:
(a) in a normal operating state, holding the first switching element in a conducting state by way of the first control device and holding the second switching element in a conducting state by way of the second control device, and
(b) in an abnormal operating state, depending on electrical properties of the first current path or of the second current path, switching the switching element which is situated in a current path having poorer electrical properties into a blocking state by way of that one of the control devices which is situated in this current path.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.